Assessing and treating autoimmune ataxia

ABSTRACT

Methods and materials herein are useful for assessing and/or treating autoimmune ataxias associated with septin-specific autoantibodies septin-5-specific autoantibodies For example, septin-5 polypeptides are provided as well as methods for using septin-5 polypeptides to detect septin-5-specific autoantibodies and/or to treat a mammal having an autoimmune ataxia.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application Ser. No. 62/674,347, filed on May 21, 2018. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application

BACKGROUND 1. Technical Field

This document relates to methods and materials for assessing and treating autoimmune ataxias associated with septin-specific autoantibodies (e.g., septin-5-specific autoantibodies). For example, this document relates to methods and materials for using septin-5 polypeptides (or fragments thereof) to detect the presence or absence of septin-5-specific autoantibodies.

2. Background Information

Cerebellar degeneration leads to disability from loss of balance, incoordination and speech impairment, and also can affect cognitive function (Hoche et al., 2017 Brain 88 (16 Supplement):206). Testing for an autoimmune cause is an important diagnostic endeavor in affected patients, particularly those with a subacute onset and rapidly progressive course (Jones et al., 2015 JAMA Neurol 72:1304-1212).

SUMMARY

This document provides methods and materials for detecting autoimmune ataxias (e.g., autoimmune cerebellar ataxias) associated with septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) as well as methods and materials for treating autoimmune ataxias associated with septin-specific autoantibodies (e.g., septin-5-specific autoantibodies).

As demonstrated herein, patients with immunotherapy-responsive autoimmune cerebellar ataxia exhibited a presence of septin-5-specific autoantibodies (e.g., septin-5-IgG) in serum and cerebrospinal fluid (CSF) samples. Also as demonstrated herein, a recombinant form of septin-5 polypeptide was able to detect the presence of septin-5-IgG in both serum and tissue.

The detection of septin-5-specific autoantibodies can be used to support a diagnosis of autoimmune ataxia associated with septin-5-specific autoantibodies, such as autoimmune cerebellar ataxias. In some eases, a septin-5 polypeptide can be used to treat autoimmune ataxia associated with septin-5-specific autoantibodies, such as autoimmune cerebellar ataxias.

In general, one aspect of this document features methods for detecting the presence or absence of a septin-5-specific autoantibody in a biological sample from a mammal. The methods can include, or consist essentially of contacting a biological sample from a mammal with a septin-5 polypeptide to form a septin-5/septin-5-specific autoantibody complex if the biological sample contains septin-5-specific autoantibodies, and detecting the presence or absence of the septin-5/septin-5-specific autoantibody complex. The method can include detecting the presence of the complex The presence of the septin-5-specific autoantibody in the biological sample can be associated with autoimmune ataxia associated with septin-5-specific autoantibodies in the mammal. The autoimmune ataxia can be an autoimmune cerebellar ataxia. The method can include performing a western blot to detect the complex. The biological sample can be whole blood, serum, plasma, or cerebrospinal fluid.

In another aspect, this document features a kit include a septin-5 polypeptide and an anti-IgG antibody. The anti-IgG antibody can be an anti-human IgG antibody. The kit anti-human IgG antibody can include a covalently attached label. The kit can include an anti-septin-5 antibody. The septin-5 antibody can be an anti-human septin-5 antibody.

In another aspect, this document features methods for treating a mammal having an autoimmune ataxia associated with septin-5-specific autoantibodies. The methods can include, or consist essentially of, withdrawing a biological fluid from the mammal, where the biological fluid contains septin-5-specific autoantibodies, contacting the biological fluid with a septin-5 polypeptide to remove a substantial portion of said septin-5-specific autoantibodies from the biological fluid, and returning the biological fluid to the mammal. The mammal can be a human. The biological fluid can include blood. The autoimmune ataxia can be an autoimmune cerebellar ataxia.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows immunofluorescence patterns of patient IgG binding to mouse tissues. A-F, patient serum produces synaptic staining patterns of: cerebellar molecular layer (ML) and granular layer (GL), A; hippocampus (Hi), B, C and D; thalamus (Th), C; cerebral cortex (Cx), D; enteric ganglia (arrow) and nerves (arrow heads), E; and renal glomeruli (arrows), F, G, mouse cerebrum proteins, reduced, denatured and separated electrophoretically produced a ˜45 KDa band when probed with patients IgGs (patient 1-6) but not healthy control subject IgGs. H and I, application of IgG eluted from a nitrocellulose strip containing the ˜45 KDa band to mouse tissue reproduced the patient IgG staining pattern Scale bar=5 mm.

FIG. 2 shows confirmation of septin-5 as a target antigen of autoimmune ataxia. A, western blot shows IgG in all 6 patients' serums binding to septin-5 recombinant protein (lanes 1-6); IgG in healthy controls' serums are non-reactive (lanes 7-9). B, confocal microscopy shows patient IgG co-localizing with septin-5 immunoreactivity in mouse cerebellum (top row) and hippocampus (bottom row). Left column; patient-IgG; middle column, commercial septin-5 IgG; tight column, merged images C, immune absorption of patient IgG by septin-5 recombinant protein: cerebellum, left column; hippocampus, right column. D, T1 sagittal MRI of head from Patient 3 demonstrating cerebellar atrophy. GL=granular layer; ML=molecular layer. Hi=hippocampus. Scale bar=5 mm.

FIG. 3 shows IgG binding to HEK293 cells transfected with expression plasmids encoding green fluorescent, protein-tagged human Septin-5 isoform 1. Commercial septin-5 antibody (A-C) and patient serum (D-F) but not healthy control serum (G-I) stain septin 5-(isoform 1)-transfected GFP-tagged HEK 293 cells. Scale bar=5 mm.

FIG. 4 shows an exemplary septin-5 polypeptide sequence (SEQ ID NO:1).

FIG. 5 shows an exemplary septin-4 polypeptide sequence (SEQ ID NO:2).

DETAILED DESCRIPTION

A specific IgG autoantibody is found in serum of patients presenting with immunotherapy-responsive autoimmune ataxias. The target of this IgG autoantibody was identified as a septin (e.g. , septin-5), a synaptic protein that functions in, for example, cytokinesis, diffusion barrier formation, release of neurotransmitters, microtubule dynamics, and host-bacterium interactions, and is found throughout the mammalian central nervous system (e.g., in the hippocampus, thalamus, and cerebellum) and the peripheral nervous system (e.g., in enteric neurons and renal glomeruli), as well as in platelets.

This document provides methods and materials for assessing and/or treating a mammal having, or suspected of having, an autoimmune ataxia. A mammal having an autoimmune ataxia associated with septin-specific autoantibodies can have an immune system that is producing septin-specific autoantibodies. For example, a mammal (e.g., a human) having an autoimmune ataxia associated with septin-5-specific autoantibodies can have an immune system that is producing septin-5-specific autoantibodies. In some cases, this document provides septin polypeptides (e.g., septin-5 polypeptides) having at least one antigenic site recognized by a septin-specific autoantibody (e.g., a septin-specific autoantibody produced by the immune system of a mammal having an autoimmune ataxia). In some cases, one or more septin polypeptides (e.g., one or more septin-5 polypeptides) provided herein can be used to detect the presence or absence septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) in a sample (e.g., a blood sample obtained from a hitman). For example, one or more septin polypeptides (e.g., one or more septin-5 polypeptides) can be used to assess a sample obtained from a mammal having, or suspected of having, an autoimmune ataxia for the presence or absence of septin-specific autoantibodies (e g., septin-5-specific autoantibodies). The presence of septin-specific autoantibodies can be used to identify (e.g., diagnose) a mammal as having an autoimmune ataxia (e.g., an autoimmune cerebellar ataxia) associated with septin-specific autoantibodies.

In some cases, one or more septin polypeptides (e.g., one or more septin-5 polypeptides) provided herein can be used to treat a mammal having, or suspected of having, an autoimmune ataxia. For example, one or more septin polypeptides (e.g., one or more septin-5 polypeptides) can be administered to a mammal having, or suspected of having, an autoimmune ataxia to treat the mammal.

Any appropriate mammal can be assessed as described herein (e.g., assessed for the presence or absence of septin-specific autoantibodies) and/or treated as described herein (e.g., treated with one or more septin polypeptides such as septin-5 polypeptides). Examples of mammals that can be assessed as described herein and/or treated as described herein include, without limitation, humans, non-human primates, monkeys, bovine species, pigs, horses, dogs, cats, rats, and mice. For example, a human can be assessed for the presence or absence of septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) as described herein. In some cases, a human identified as having an autoimmune ataxia and as having septin-specific autoantibodies can be treated with one or more septin polypeptides (e.g., septin-5 polypeptides) as described herein.

Any appropriate sample from a mammal (e.g., a human) can be assessed as described herein (e.g., assessed for the presence or absence of septin-specific autoantibodies). Examples of samples (e.g., biological samples) that can be assessed as described herein include, without limitation, biological fluids (e.g., blood such as whole blood, serum, or plasma, urine, cerebrospinal fluid, synovial fluid, or saliva) and biological tissues (e.g., brain tissue such as tissue obtained from a brain biopsy). For example, serum can be obtained from a mammal and assessed for the presence or absence of septin-specific autoantibodies (e.g., septin-5-specific autoantibodies).

A mammal having any appropriate type of autoimmune ataxia can be assessed (e.g., for the presence or absence of septin-specific autoantibodies such as septin-5-specific autoantibodies) and/or treated (e.g., by administering a septin polypeptide to the mammal) using the methods and materials described herein. In some cases, an autoimmune ataxia can be a severe ataxia. In some cases, an autoimmune ataxia can be a rapidly progressive ataxia. In some cases, an autoimmune ataxia can be a paraneoplastic ataxia (e.g., can be associated with, can be a symptom of, or can be a complication of a cancer). For example, an autoimmune ataxia can be associated with a neuroendocrine tumor (e.g., neuroendocrine pancreatic tumor). An autoimmune ataxia can affect any appropriate pan of a mammal's nervous system (e.g., a part of the nervous system that coordinates movement) such as the cerebellum (e.g., cerebellar ataxia), dorsal columns (e.g., sensory ataxia), or vestibular system (e.g., vestibular ataxia). In some cases, an autoimmune ataxia can be art autoimmune cerebellar ataxia. For example, a mammal having an autoimmune cerebellar ataxia can be assessed and/or treated using the methods and materials described herein.

Any appropriate septin polypeptide can be used as described herein (e.g., to detect the presence or absence septin-specific autoantibodies and/or to treat a mammal having, or suspected of having, an autoimmune ataxia). For example, in humans, a septin polypeptide can be a septin-1 polypeptide, a septin-2 polypeptide, a septin-3 polypeptide, a septin-4 polypeptide, a septin-5 polypeptide, a septin-6 polypeptide, a septin-7 polypeptide, a septin-8 polypeptide, a septin-9 polypeptide, a septin-10 polypeptide, a septin-11 polypeptide, a or septin-12 polypeptide. In some cases, a septin polypeptide can be a septin-5 polypeptide. In some cases, a septin polypeptide can be a septin-4 polypeptide. In some cases, a full length septin polypeptide (e.g., a full length septin-5 polypeptide) can be used to assess a sample for the presence or absence of septin-specific autoantibodies such as septin-5-specific autoantibodies. In some cases, a fragment of a septin polypeptide (e.g., a fragment of a septin-5 polypeptide) can be used to assess a sample for the presence or absence of septin-specific autoantibodies such as septin-5-specific autoantibodies. For example, a fragment of a septin polypeptide containing one or more epitopic sites (e.g., B cell epitopes) can be used to assess a sample for the presence or absence of septin-specific autoantibodies such as septin-5-specific autoantibodies. Examples of fragments of a septin polypeptide that can be used to assess a sample for die presence or absence of septin-specific autoantibodies include, without limitation, those fragments set for this Table 1.

TABLE 1 Human septin polypeptide fragments. First amino acid Last amino acid Name of septin-4 fragment residue^(#) residue^(#) J3QRS4_Human 21 72 First amino acid Last amino acid Name of septin-5 fragment residue^(##) residue^(##) F8W9E5_Human 48 227 C9JM82_Human 48 301 E7QM7_Human 1 248 ^(#)numbering is based on amino acid sequence of Genbank Accession Number NP_004565.1. ^(##)numbering is based on amino acid sequence of Genbank Accession Number NP_002679.2.

In some cases, a septin-4 polypeptide can be used as described herein (e.g., to detect the presence or absence septin-specific autoantibodies and/or to treat a mammal having, or suspected of having, an autoimmune ataxia). Examples of septin-4 polypeptide sequences (and the nucleic acids encoding such polypeptides) can be found in the National Center for Biotechnology Information (NCBI) databases (e.g., Gen Pept and GenBank). Examples of human septin-4 polypeptide sequences include, without limitation, NCBI Accession Nos NP_536341 (Version No. NP_536341.1), NP_004565 (Version No. NP_004565.1), NP_536340 (Version No. NP_536340.1), and NP_001185642 (Version No. NP_001185642.1). Additional septin-4 sequences can be found, for example, in public databases. A representative human septin-4 sequence is as shown in FIG. 5 (SEQ ID NO:2). In some cases, a fragment of a septin-4 polypeptide can be used as described herein. Examples of fragments of septin-4 fragments that can be used to detect a septin-4-specific autoantibody can include, without limitation, those fragments set forth in Table 1.

In some cases, a septin-5 polypeptide can be used as described herein (e.g., to detect the presence or absence septin-specific autoantibodies and/or to treat a mammal having, or suspected of having, an autoimmune ataxia). A septin-5 polypeptide can be any appropriate isoform of septin-5. In some cases, a septin-5 can be a septin-5-variant 1 (v1) (e.g., a full-length septin-5 polypeptide). In some cases, a septin-5 can be a septin-5 v2 (e.g., a septin-5 polypeptide having a truncated N-terminus). Examples of septin-5 polypeptide sequences (and the nucleic acids encoding such polypeptides) can be found in the NCBI databases (e.g., Gen Pept and GenBank). Examples of human septin-5 polypeptide sequences include, without limitation, NCBI Accession Nos. NP_002679 (Version No. NP_002679.2; SEQ ID NO:1), NP_001009939 (Version No. NP_001009939.1), and AHW56397 (Version No. AHW56397.1). Additional septin-5 sequences can be found, for example, in public databases. A representative human septin-5 sequence is as shown in FIG. 4 (SEQ ID NO:1). In some cases, a fragment of a septin-5 polypeptide can be used as described herein Examples of fragments of septin-5 polypeptides that can be used to detect a septin-5-specific autoantibody can include, without limitation, those set forth in Table 1.

This document also provides nucleic acids and constructs encoding septin polypeptides described herein (e.g., septin-5 polypeptides) or fragments of septin polypeptide described herein. As used herein, nucleic acid can refer to RNA, DNA, or a combination thereof. In some cases, a nucleic acid encoding a septin polypeptide or fragment of a septin polypeptide described herein can be an isolated nucleic acid. As used herein wish respect to nucleic acids, “isolated” refers to (i) a nucleic acid sequence encoding all or pan of a septin polypeptide, but free of coding sequences that normally flank one or both sides of the nucleic acid sequences encoding the septin in the genome, or (ii) a nucleic acid incorporated into a vector or into the genomic DNA of an organism such that the resulting molecule is not identical to any naturally-occurring vector or genomic DNA in some cases, a nucleic acid provided herein can encode a fragment of a septin polypeptide where the fragment is a fragment set forth in Table 1.

In some cases, a septin polypeptide that can be used as described herein (e.g., to detect the presence or absence septin-specific autoantibodies and/or to treat a mammal having, or suspected of having, an autoimmune ataxia) can have a sequence that deviates from a wild type septin polypeptide sequence, sometimes referred to as a variant sequence. For example, a septin polypeptide sequence can have at least 80% sequence identity to SEQ ID NO:1 provided that it includes one or more amino acid additions, subtractions, or substitutions compared to SEQ ID NO:1. In some embodiments, a septin polypeptide sequence can have at least 85% sequence identity, 90% sequence identity, 95% sequence identity, or at least 99% sequence identity to SEQ ID NO: 1 provided that it includes one or more amino acid additions, subtractions, or substitutions compared to SEQ ID NO:1. Percent sequence identity is calculated by determining the number of matched positions in aligned nucleic acid or polypeptide sequences, dividing the number of matched positions by the total number of aligned nucleotides or amino acids, respectively, and multiplying by 100. A matched position refers to a position in which identical nucleotides or amino acids occur at the same position in aligned sequences. The total number of aligned nucleotides or amino acids refers to the minimum number of septin nucleotides or amino acids that are necessary to align the second sequence, and does not include alignment (e.g., forced alignment) with non-septin sequences, such as those fused to septin The total number of aligned nucleotides or amino acids may correspond to the entire septin sequence or may correspond to fragments of the full-length septin sequence as defined herein.

Sequences can be aligned using the algorithm described by Altschul et al. (Nucleic Acids Res., 25:3389-3402 (1997)) as incorporated into BLAST (basic local alignment search tool) programs, available at ncbi.nlm.nih.gov on the World Wide Web. BLAST searches or alignments can be performed to determine percent sequence identity between a septin nucleic acid molecule and any other sequence or portion thereof using the Altschul et al. algorithm. BLASTN is the program used to align and compare the identity between nucleic acid sequences, while BLASTP is the program used to align and compare the identity between amino acid sequences. When utilizing BLAST programs to calculate the percent identity between a septin sequence and another sequence, the default parameters of the respective programs are used.

A septin polypeptide (or fragment thereof) that can be used as described herein (e.g., to defect the presence or absence septin-specific autoantibodies and/or to treat a mammal having, or suspected of having, an autoimmune ataxia) can be from any appropriate source. In some cases, a septin polypeptide (or fragment thereof) described herein can be obtained from human, mouse, or other mammalian neuronal tissue, neuronal cell lines, or transfected cells (e.g., mammalian, E. coli or yeast) expressing a recombinant septin nucleic acid, or the septin polypeptide may be synthetic. In some cases, a septin polypeptide (or fragment thereof) described herein can be in a cell lysate (e.g., a whole cell lysate or a cell fraction). In some cases, a septin polypeptide (or fragment thereof) described herein can be a purified polypeptide. A “purified” polypeptide refers to a polypeptide that constitutes the major component in a mixture of components, e.g., 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 99% or more by weight. Polypeptides may be purified by methods including affinity chromatography or immunosorbent affinity column. Such methods can be modified to increase the solubility of the polypeptide, and purified polypeptides can be examined for their immunogenicity using methods such as western blot or immunoprecipitation assays.

For fragments of a septin polypeptide, the fragment can be generated using any appropriate method. For example, given a septin polypeptide sequence (e.g., a septin-5 polypeptide sequence), any appropriate polypeptide fragment can be generated by, for example, proteolytic cleavage of a polypeptide or chemical synthesis.

This document also provides methods tor detecting septin-specific autoantibodies (e.g., septin-5-specific autoantibodies). The presence of septin-specific autoantibodies can be used to diagnose an autoimmune ataxia associated with septin-specific autoantibodies. For example, the methods and materials described herein can be used to identify a mammal (e.g., a human) as having an autoimmune ataxia associated with septin-specific autoantibodies (e.g., having an immune system that is producing septin-specific autoantibodies) based, at least in part, on the presence of septin-specific autoantibodies in a sample obtained from the mammal. In some cases, a septin polypeptide (e.g., a septin-5 polypeptide) (or fragment thereof) described herein can be used (e.g., in various immunological techniques) to detect a septin-specific autoantibody (e.g., a septin-5-specific autoantibody). For example, a septin-5 polypeptide (or fragment thereof) described herein can be used in an immunoassay to detect septin-5-specific autoantibodies in a biological sample in some cases, septin polypeptides (or fragment thereof) described herein can be contacted with a sample (e.g., serum) obtained from a mammal (e.g., a mammal suspected of having an autoimmune ataxia associated with septin-specific autoantibodies) under conditions where, when septin-specific autoantibodies are present, the septin polypeptides (or fragments thereof) can form a complex with the septin-specific autoantibodies (e.g., a septin/septin-specific autoantibody complex), and an immunoassay can be used to detect the complex. For example, when septin-5-specific autoantibodies are present in a sample obtained from a mammal suspected of having an autoimmune ataxia, a septin-5 polypeptide (or fragment thereof) described herein cast be used to form a complex with the septin-5-specific autoantibodies (e.g., a septin-5/septin-5-specific autoantibody complex), and an immunoassay can be used to detect the complex. Examples of immunoassays that can be used to detect the presence of a septin-specific autoantibody, or a septin/septin-specific autoantibody complex include, without limitation, immunocytochemical staining techniques, immunohistochemical staining techniques, enzyme-linked immunosorbent assays (ELISA), western blot, radioimmunoassays, cell-based immunofluorescence assays, and flow cytometry.

Septin polypeptides (or fragments thereof) that can be used as described herein (e.g., to detect the presence or absence septin-specific autoantibodies and/or to treat a mammal having, or suspected of having, an autoimmune ataxia) with or without modification. In some cases, a septin polypeptide (or fragment thereof) can be modified for the detection of septin-specific autoantibodies in vitro (e.g., in an immunoassay). In some cases, a septin polypeptide (or fragment thereof) can be modified for the detection of septin-specific autoantibodies in vivo (e.g., in an in vivo imaging technique). Polypeptides (or fragment thereof) can be labeled by either covalently or non-covalently combining the polypeptide with a second substance that provides for detectable signal. A wide variety of labels and conjugation techniques can be used. Some examples of labels that can be used include radioisotopes, enzymes, substrates, cofactors, inhibitors, fluorescent agents, chemiluminescent agents, magnetic particles, and the like. In some cases, a septin polypeptide (or fragment thereof) can be conjugated to an imaging agent. Suitable imaging agents include, but are not limited to, radioisotopes, such as ³²P, ⁹⁹Tc, ¹¹¹In and ¹³¹I.

In some cases, anti-septin antibody (e.g., an anti-septin-5 antibody) can be used in various immunological techniques for detecting septin polypeptides (e.g., septin-5 polypeptides). In some cases, an anti-septin-5 antibody can be used (e.g., in various immunological techniques) to detect a septin-5 polypeptide. For example, an anti-septin-5 antibody can be used in an immunoassay to detect a septin-5 polypeptide. In some cases, when septin-specific autoantibodies are present in a sample, septin polypeptides can form a complex with the septin-specific autoantibodies (e.g., a septin/septin-specific autoantibody complex), and an immunoassay using an anti-septin antibody can be used to detect the complex. Examples of immunoassays that can be used to detect the presence of a septin polypeptide, or a septin/septin-specific autoantibody complex, include, without limitation, immunocytochemical staining techniques, immunohistochemical staining techniques, ELISA, western blot, radioimmunoassays, cell-based immunofluorescence assays, and flow cytometry.

Anti-septin antibodies (e.g., anti-septin-5 antibodies) can be used with or without modification for the detection of septin polypeptides (e.g., septin-5 polypeptides). Anti-septin antibodies can be labeled either directly or indirectly, and a wide variety of labels, including radioisotopes, enzymes, substrates, cofactors, inhibitors, fluorescent agents, chemiluminescent agents, and magnetic particles. In some cases, an anti-septin antibody having specific binding affinity for a septin polypeptide can be conjugated to an imaging agent. Examples of imaging agents that can be used include, without limitation, radioisotopes, such as ³²P, ⁹⁹Tc, ¹¹¹In, and ¹³¹I.

In some cases, a mammal identified as having an autoimmune ataxia associated with sept in-specific autoantibodies (e.g., having an immune system that is producing septin-specific autoantibodies) as described herein (e.g., based, at least in pan, on the presence of septin-specific autoantibodies in a sample obtained from the mammal) can have the diagnosis confirmed. For example, identification of an autoimmune ataxia can be confirmed using, for example, physical examinations such as a neurological examination (e.g., for memory, concentration, vision, hearing, balance, coordination, and/or reflexes) and imaging studies such as brain imaging studies (e.g., computer tomography (CT) scanning and magnetic resonance imagining (MRI)).

This document also provides methods for treating a mammal (e.g., a human) identified as having an autoimmune ataxia (e.g., whose immune system is producing septin-specific autoantibodies such as septin-5-specific autoantibodies) In some cases, methods for treating a mammal (e.g., a human) identified as having an autoimmune ataxia associated with the presence of septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) can be effective to reduce one or more symptoms of the autoimmune ataxia Examples of symptoms of autoimmune ataxias include, without limitation, neurobehavioral phenotypes, cortical dysplasia, developmental delays, platelet dysfunction, pain, fatigue, dizziness, incoordination (e.g., resulting in falls), gait difficulties, and speech difficulties, tri some cases, methods for treating a mammal (e.g., a human) identified as having an autoimmune ataxia associated with the presence of septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) can be effective to remove a substantial portion of septin-specific autoantibodies present within the mammal (e.g., present within a body fluid of the mammal). As used herein, removing a “substantial portion” means removing at least 20% (e.g., at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 93%, at least 95%, at least 96%. at least 97%, at least 98%, at least 99%, at least 99.5%, at least 99.8%, or even 100%) of the septin-specific. autoantibodies (e.g., septin-5-specific autoantibodies) that were present in the body fluid of a mammal prior to treating the mammal as described herein. The body fluid can be blood (e.g., serum or plasma) or any other body fluid, e.g., lymph or cerebrospinal fluid. In some cases, depleting septin-specific autoantibodies (e.g., septin-5-specific autoantibodies)from mammals with a autoimmune ataxia as described herein also can be effective to reduce one or more symptoms of the autoimmune ataxia.

In some cases, a mammal identified as having an autoimmune ataxia can be treated by administering to the mammal any appropriate agent or therapy used to treat an autoimmune ataxia. In some cases, art agent or therapy used to treat an autoimmune ataxia can treat one or more symptoms of an autoimmune ataxia. Examples of agents and therapies that can be used to treat ataxia include, without limitation, immunomodulatory agents such as immunosuppressants (e.g., corticosteroids, mycophenolate mofetil, azathioprine, tacrolimus, cyclophosphamide, rituximab, mTOR inhibitors, methotrexate, anti-CD19 monoclonal antibodies, and anti-II-6 monoclonal antibodies), physical therapy, occupational therapy, and speech therapy. In some cases, septin antigen specific tolerance induction strategies or immunotherapy targeting septin-specific T cells and/or B cells can be used to treat an autoimmune ataxia associated with septin-specific autoantibodies.

In some cases, a mammal identified as having an autoimmune ataxia associated with the presence of septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) can be treated using one or more septin polypeptides (e.g., one or more septin-5 polypeptides) described herein (e g, in an apheresis method) For example, apheresis for the treatment of an autoimmune ataxia associated with septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) can be used to remove septin-specific autoantibodies front a human. Methods and extracorporeal systems for apheresis (i.e., the process of withdrawing blood from a mammal, removing components from the blood, and returning the blood, or blood depleted of one or more components, to the mammal) can be used as described elsewhere (see, for example, U.S. Pat. Nos. 4,708,713; 5,258,503; 5,386,734; and 6,409,696). In some cases, an apheresis method can be used to remove septin-specific autoantibodies from a body fluid of a mammal. The method can include withdrawing a body fluid from a mammal; removing a substantial portion of septin-specific autoantibodies from the fluid; and returning the fluid to the mammal. Antibodies removed can be of any class, e.g., IgG (such as IgG1, IgG2, IgG3, IgG4), IgM, IgD, IgA, or IgE antibodies.

Removal of septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) can be performed by contacting a body fluid with one or more septin polypeptides (e.g., septin-5 polypeptides) described herein. The septin polypeptide can be bound to a solid support. Such solid supports cast be, without limitation, membranes, fibers, spherical beads, or granules and can be made with a water-insoluble, preferably porous, biocompatible material, e.g., organic polymers such as agarose, dextran, and polyacrylamide, or inorganic porous materials such as porous glass or porous silica gel. Such materials can be used as is or adapted (e.g., derivatized with appropriate chemical groups) for attachment of a septin polypeptide.

When the body fluid is blood, the plasma and/or white blood cells can be separated from red blood cells (e.g., erythrocytes), and the red blood cells can be returned to the mammal with or without white blood cells. In some cases, the blood cells are returned to the mammal with artificial rather than their original blood plasma. The “replacement fluid” (e.g., physiological saline) can be administered to the mammal after removal of the fluid. In some cases, the septin-specific autoantibodies (e.g., septin-5-specific autoantibodies) can be selectively removed from the blood plasma in the course of apheresis, and the blood cells can be mixed with the septin-specific autoantibody-depleted plasma and then re-infused as a mixture into the mammal.

The system can be a continuous one in which, for example, blood is pumped out of a blood vessel (e.g., an artery or a vein) passed over a solid support derivatized with septin polypeptides (e.g., septin-5 polypeptides) described herein and pumped directly back into a blood vessel of the mammal. As in non-continuous systems, blood cells can be separated from plasma prior to passing of the plasma over the solid support.

In cases where septin polypeptides (e.g., septin-5 polypeptides) described herein are used in an apheresis method to treat a mammal (e.g., a human) having an autoimmune ataxia, the methods also can include administering to the mammal any appropriate agent or therapy used to treat an autoimmune ataxia described herein In cases where a mammal having an autoimmune ataxia is treated with one or more septin polypeptides described herein and is treated with agents or therapies used to treat an autoimmune ataxia described herein, the agents or therapies used to treat an autoimmune ataxia can be administered at the same time or independently. For example, one or more septin polypeptides described herein and one or more agents or therapies used to treat an autoimmune ataxia can be formulated together to form a single composition. In some cases, one or more septin polypeptides described herein can be administered first, and the one or more agents or therapies used to treat an autoimmune ataxia administered second, or vice versa.

This document also provides articles of manufacture (e.g., kits) containing one or more septin polypeptides described herein (e.g., one or more septin-5 polypeptides described herein). Septin polypeptides (e.g., septin-5 polypeptides) described herein that are included in an article of manufacture as described herein can be provided within a cell, in a solution in which they are soluble, or in a lyophilized form. The kit may further include a second substance that, for example, provides for detection of a septin polypeptide/anti-septin autoantibody complex. Such substances can be an anti-septin antibody (e.g., an anti-septic-5 antibody), an anti-IgG antibody (e.g., an anti-human IgG antibody), or combinations thereof. Such substances can include a covalently linked detectable label (e.g., a fluorescent label). In addition, a kit can include directions for using the septin polypeptides and/or directions for practicing a method described herein (i.e., detecting septin-specific autoantibodies in a biological sample). For example, a kit can include directions for using the septin-5 polypeptides and/or directions for practicing a method described herein (e g., detecting septin-5-specific autoantibodies in a biological sample).

The invention will be further described in the following examples, which do not limit the scope of the invention described in the claims.

EXAMPLES Example 1: Autoimmune Septin-5 Cerebellar Ataxia Patients and Methods Study Population

367 archived specimens (serum, 334. CSF, 33) from patients for whom tissue-based immunofluorescence assay (IFA) screening had demonstrated a pattern of diffuse neural synaptic (neuropil) antibody staining resembling, but not meeting criteria for, amphiphysin-IgG (as described in, for example, Honorat et al., 2017 Neurol Neuroimmunol Neuroinflamm 4:e385). Archived specimens with that designation were retested by IFA and classified according to their staining patterns Clinical information was obtained by medical record review.

Antigen Preparation

Cytosolic and membrane preparations were used. For the cytosolic antigen preparation, adult mouse cerebellum and cerebrum were homogenized with buffer, 2 ml/g (10 mM Hepes, 1 mM MgCl₂, 1 mM ethylenediaminetetraacetic acid, and complete protease inhibitor cocktail [Roche, Indianapolis, USA]). Homogenate was clarified by centrifugation (50000×g, 15 minutes) and supernatant was stored at −80° C. For the membrane preparation, pellet front the cytosolic preparation was resuspended in NP-40 buffer (1% NP-40, 0.1% SDS, 0.15M NaCl, 0.01M NaPO₄ pH 7.2, 2 mM EDTA, and complete protease inhibitor cocktail [Roche, Indianapolis, USA]) for 2 hours then centrifuged at 100000×g for 45 minutes. Supernatant was stored at −80° C.

Western Blotting, Immunoprecipitation, & Mass Spectrometry

For western blot, mouse cytosolic or membrane cerebellar extract was separated on 4-15% or 10% polyacrylamide gels, and the membrane was probed with sera from healthy subjects and patients (1:200 dilution), and commercial septin-5-specific IgG (1:5000). Recombinant full length septin-4, septin-5 and septin-7 proteins were used for western blot (Abcam, San Francisco, Calif., USA).

For immunoprecipitation, serum of 2 patients (patients 2 and 6) was pooled then IgG was purified using protein G sepharose. The IgG were eluted from the protein G complex by acetic acid and dialyzed using a 10000 MCWO membrane (Thermo Scientific, Rockford, Ill., USA) in PBS then HEPES buffer. The collected IgG was bound to Affi-GeI (9:1.5 ratio) rotating at 4° C. for 4 hours (Bio-Rad, Hercules, Calif., USA). The complex was washed in various buffers (NP-406Murea, then again in NP-40) and exposed to cerebellar membrane protein extract (overnight, 4° C.). After washing, the antigen was eluted with 6M urea buffer (6M urea, 2% Chaps). The eluted sample was electrophoresed using a 10% polyacrylamide gel, and proteins were located by silver staining and by western blot. The immunoreactive bands were excised from the stained gel and analyzed by high pressure liquid chromatography electrospray tandem mass spectrometry.

Plasmid Constructs

Human full-length SEPT5 cDNAs were cloned into pcDNA3.1+/C−(K)DYK+N−eGFP (green fluorescent protein) vectors (GenScript, Piscataway, N.J. USA). All of the plasmid constructs were verified by Sanger DNA sequencing.

Cell Based Immunofluorescence Assay (CBA)

HEK293 cells stably transfected with GFP-tagged Sept5 cDNA (isoform I) were generated and used for CBA. Cells were plated in 8-well poly-D-lysine-coated chamber slides (Corning, Corning, N.Y.), fixed in 4% paraformaldehyde and permeabilized with Triton-X-100. Patient or control serum (1:200 dilution), CSF (1:10) or commercial septin-5-IgG (1:500) were added to the cells for 45 to 60 minutes at room temperature. Secondary antibody (TRITC—conjugated goat antihuman, anti-rabbit or anti-mouse IgG, 1:400) was applied for 30 minutes.

Protein Microarray

This experiment was conducted by ThermoFischer Scientific utilising the Human ProtoArray v.5.0; Invitrogen Nine thousand purified human proteins were printed in nitrocellulose-coated microarray slides. The slides were blocked in blocking buffer (50 mM HEPES, 200 mM NaCl, 0.01% Triton X-100, 25% glycerol, 20 mM reduced glutathione, 1.0 mM DTT, 1× synthetic block) at 4° C. for 1 hour. The slides were rinsed in PBST buffer then probed with serum from patients or controls (1:500) for 90 minutes at 4° C. with gentle agitation The slides were washed 5 times and incubated (90 minutes, 4° C.) with an Alexa Fluor 647-conjugated goat anti-human IgG antibody (1 μg/ml). The slides were washed and dried by spinning. The microarray slides were then scanned using a GenePix 4000B fluorescent microarray scanner.

RESULTS Characterisation of the Antigen  Immunohistochemical Distribution of the Neural Antigen

Indirect IFA of patients' serums and CSF using cryosections of murine brain tissue demonstrated a novel identical staining pattern in 6 patients (FIG. 1A-1F). Specimens strongly stained synaptic regions (neuropil) of mouse cerebrum and cerebellum. The molecular layer of the cerebellum and the thalamus demonstrated stronger immunoreactivity than midbrain, hippocampus, cortex and basal ganglia. The myenteric plexus of the gastric mucosa and the renal glomeruli were also reactive in all cases. The staining pattern superficially resembled that produced by gamma amino butyric acid (GARA)_(B) receptor antibody; all were negative by cell-based assay (CBA) for that antibody.

 Identification and Confirmation of Septin-5 as Antigen

Immunoblotting of mouse brain lysates with serums revealed a common immunoreactive band with approximate molecular weight of 45 kDa among patients only (FIG. 1G). A patient serum and purified IgG eluted from that patient's 45 kDa demonstrated the same pattern of IgG staining by IFA (FIGS. 1H and 1I). To identify the target antigen, immunoprecipitation of mouse cerebellar extract was performed using IgGs from patients 2 and 6. Analysis by in-gel digestion and mass spectrometry of proteins captured by IgGs from those 2 patients, immobilized by Affi-Gel, assigned the greater number of polypeptides to septin-5 (43 kDa).

In order to confirm septin-5 as the antigen of interest, firstly, a recombinant form of septin-5 protein was used for western blot analysis and probed with serum. Serums from patients 1 to 6, but not control serums, demonstrated strong immunoreactivity with septin-5 (FIG. 2A). Secondly, IFA demonstrated co-localization between commercial septin-5 IgG and patient-IgG on mouse brain tissue (FIG. 2B). Thirdly, mouse brain immunoreactivity of patients' IgG was abrogated by the absorption of a patient's serum with septin-5 recombinant protein (FIG. 2C). Fourthly, patients' serums and CSF were tested by indirect IFA on septin-5-transfected BEK 293 cells (CBA, FIG. 3 ). Serums and CSF of all 6 patients were reactive with septin-5 (isoform 1 only), and all controls were negative. Finally, the screening protein microarray was used in a blinded fashion to analyze the antibody profiles in serums available from 5 of the 6 patients (patients 1-5) and 5 controls (healthy and known to be neural antibody negative in our laboratory). Candidate autoantigens are shown in Table 1.

TABLE 1 Candidate autoantigens with elevated signal in the Group 1 (Disease) samples relative to the Group 2 (Normal) samples. Count Mean Disease Normal Relative fluorescence units Ratio Group, Group, P- Negative Disease Normal (Disease/ Database ID N N Value Cutoff Signal Group Group Normal) Protein name (Gene ID) NM_002688.2 5 0 0.004 3031 104 47020 2086 22.5 Septin 5 (SEPT5) NM_004574.2 4 0 0.024 946 48 11296 523 21.6 Septin 4 (SEPT4), transcript variant 1 BC029220.1 4 0 0.024 4400 125 21173 2237 9.5 Transcription factor SOX-5 NM_198266.1 5 1 0.024 2343 239 19490 2182 8.9 Inhibitor of growth family, member 3 (ING3), transcript variant 2 BC015752.1 4 0 0.024 1500 42 7306 843 8.7 Interferon regulatory factor 4 (IRF4) NM_001005339.1 5 1 0.024 2557 487 19932 2455 8.1 Regultor of G-protein signaling 10 (RGS10), transcript variant 1 NM_024946.1 5 0 0.004 4179 113 22185 2916 7.6 NEFA-interacting nuclear protein NIP30 (NIP30) NM_014110.3 4 0 0.024 5988 539 32701 4332 7.5 Protein phosphatase 1, regulatory (inhibitor) subunit 8 (PPP1R

), transcript variant 1 BC040946.1 4 0 0.024 4224 211 19544 2697 7.2 CWC15 homolog (S. cerevisiae) (HSPC148) NM_001007246.

4 0 0.024 2819 72 8765 1391 6.3 Bromodomain and WD repeat domain containing 1 (BRWD1), transcript variant 3 BC047064.1 4 0 0.024 1904 732 9199 1463 6.3 SRY (sex determining region Y)- box 6, mRNA (cDNA clone MGC: 48285 IMAGE: 5269193), complete cds NM_207350.1 4 0 0.024 2112 47 7167 1196 6.0 Similar to FRG1 protein (FSHD region gene 1 protein) (MGC72104) NM_001788.3 4 0 0.024 979 57 2815 476 5.9 Septin 7 (SEPT7), transcript variant 1 NM_130777.1 4 0 0.024 3065 74 8141 1409 5.8 X antigen family, member 2 (XAGE2) BC005004.1 4 0 0.024 3018 532 9406 1685 5.6 family with sequence similarity 64, member A (FAM64A) BC015803.1 4 0 0.024 3241 211 10759 2138 5.0 interferon regulatory factor 2 (IRF2) NM_138640.1 4 0 0.024 2589 75 88

9 1768 5.0 golgi associated, gamma adaptin ear containing, ARF binding protein 2 (GGA2), transcript variant 2 NM_153498.1 4 0 0.024 2105 66 4822 1064 4.5 calcium/calmodulin-dependent protein kinase ID (CAMK1D), transcript variant 2 NM_014891.1 4 0 0.024 7880 3421 21504 4850 4.4 PDGFA associated protein 1 (PDAP1) NM_002904.4 4 0 0.024 6903 5463 15464 3957 3.9 RD RNA binding protein 1 (RDBP) BC051687.1 4 0 0.024 3119 63 6520 1704 3.8 Kruppel-like factor 3 (basic) (KLF3) BC066938.1 5 1 0.024 2268 323 9704 2580 3.8 DEAD (Asp-Gl

-Ala-Asp) box polypeptide 43 (DDX43) BC051733.1 4 0 0.024 3099 112 5755 1581 3.6 Leucine zipper protein 1, mRNA (cDNA clone MGC: 51018 IMAGE: 4838475), complete cds NM_005720.1 4 0 0.024 1293 54 2854 810 3.5 actin related protein 2/3 complex, submit 1B, 41 kDa (ARPC1B) BC050616.1 4 0 0.024 1316 337 2368 762 3.1 tumor suppressing subtransferable candidate 4 (TSSC4) BC008288.1 5 1 0.024 953 50 2758 902 3.1 UBX domain containing 1 (UBXD1) BC014924.1 4 0 0.024 6634 783 10051 3940 2.6 kinesin family member 2C (KIF2C) BC013009.1 4 0 0.024 1789 50 3080 1304 2.4 zinc finger, MYM-type 3 (ZMYM3) NM_001156.2 4 0 0.024 1473 35 2508 1129 2.2 annexin A7 (ANXA7), transcript variant 1 NM_002596.2 4 0 0.024 1862 391 2329 1137 2.0 PCTAIRE protein kinase 3 (PCTK3), transcript variant 3, mRNA NM_178425.1 4 0 0.024 1576 92 2022 1005 2.0 histone deacetylase 9 (HDAC9), transcript variant 5

indicates data missing or illegible when filed

Septin-5 was identified as the top candidate autoantigen among all patient serums, and was not a candidate antigen in any of the controls. In each patient serum, septin-5 had the highest fold change in signal intensity relative to the controls and the lowest p-value. Because septin-4 and septin-7 were also identified as possible lower probability candidates, western blots utilizing recombinant forms of those proteins were undertaken using all 6 patient serums. Patient 3 alone had septin-4-IgG detected.

Clinical Features

Four of the 6 patients were female. The median age of symptom onset was 59 years (range, 47-62). The median septin 5-IgG antibody value in serum for the 6 patients was 1:15360 (range, 1:7680-1:15,360; normal value≤120)

Clinical information was available for 4 patients (2 men, 2 women; Table 2), median follow-up duration was 35 months (range, 1-77).

TABLE 2 Clinical, testing, treatment and outcome data for 4 patients with autoimmune septin-5 cerebellar ataxia. Patient Coexisting Coexisting Inflammatory

/Sex/Age/ Septin-5 antibodies autoimmune CSF MRI Race Clinical summary Cancer Ig-G+ (

/L) disease finding brain 2/F/60/C Subacute onset No Serum None No NA Normal vertigo, intractable & CSF nausea and vomitting. initially diagnosed as

follwowed by

 ataxia 3/M/62/NA Rapidly progressive NA Serum GAD65 0.17 NA NA NA eye movement & CSF Septin-4 disorder.

, followed by

pathy 4/F/59/AA Rapidly progressive No Serum CCN 0.06 No NA NA spinocerebellar (investigations & CSF syndrome with

including age- related cancer screening & PET scan) 5/M/47/C Headache followed by No Serum CCN 0.14. No Protein Cerebellar subacute cerebellar (investigations (CSF GAD65 28.1 70 mg/dL;

ataxia, & prominent including age- NA) elevated IgG atrophy

related cancer synthesis rate screening, & CT body, & ultrasound of testes) Disease- duration (symptom Patient onset to last

/Sex/Age/ Immunotherapy Neurologic Neurologic mRS at follow up/ Race (Improved?)

last F/U death, months) 2/F/60/C None, resolved Use of Ambulated 0 77 spontaneously walker independently 3/M/62/NA NA NA NA NA 1 4/F/59/AA Oral steroids. Bedbound Death 6 6 PLEX (initially) 5/M/47/C IVMP followed Use of Ambulated 1 54 by IVIg cane independently, maintenance with residual (Yes) atasic signs AA = African-American; C = Caucasian; CCN = N-type calcium channel antibody; CT = computerized tomography; F = female; F/U = follow-up; GAD65 = glutamic acid decarboxylase, 65 kDa isoform; IVMP = intravenous methylprednisolone; IVIg = intravenous immune globulin; M = male; mRS = modified Rankin score; NA = not available; NO. = number; PET = positron emission tomography; PLEX = plasma exchange.

indicates data missing or illegible when filed All 4 patients bad a cerebellar syndrome of subacute onset and rapid progression. One patient bad severe vertigo, nausea and vomiting at onset, before developing a rapidly progressive cerebellar ataxia. Two other patients had prominent oscillopsia at onset. Two patients had accompanying tremulousness. One patient became encephalopathic and obtunded later in the clinical course. The one patient with routine CSF parameters available had an elevated IgG synthesis rate. Head MRI (available in 2) demonstrated cerebellar atrophy in 1 (FIG. 2D) and was unremarkable in 1. None had cancer identified. One patient spontaneously recovered. Immunotherapies employed in 2 other patients with treatment and outcome data available included corticosteroids (2), plasma exchange (1), and intravenous immune globulin (1). Improvements were robust and sustained in 1 patient and transient in one (the patient died 6 months later).

OTHER EMBODIMENTS

It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims. 

1-15. (canceled)
 16. A method, comprising: (a) contacting a biological sample from a patient having or suspected of having immunotherapy-responsive autoimmune cerebellar ataxia with a septin-5 polypeptide to form a septin-5/septin-5-specific autoantibody complex if said biological sample contains septin-5-specific autoantibodies; (b) detecting the presence or absence of said complex; and (c) treating the patient when the presence of said complex is detected.
 17. The method of claim 16, wherein said method comprises performing a western blot to detect said complex.
 18. The method of claim 16, wherein said biological sample is selected from the group consisting of whole blood, serum, plasma, and cerebrospinal fluid.
 19. The method of claim 16, wherein the patient has septin-5-specific autoantibodies.
 20. The method of claim 16, wherein step (c) comprises treating the patient with one or more septin-5 polypeptides.
 21. The method of claim 20, wherein treating the patient comprises depleting septin-5-specific autoantibodies from the patient.
 22. The method of claim 21, wherein step (c) is effective to reduce one or more symptoms of the autoimmune ataxia.
 23. The method of claim 16, wherein step (c) comprises: i) withdrawing a body fluid from the patient; ii) removing a substantial portion of septin-5-specific autoantibodies from the fluid; and iii) returning the fluid to the patient.
 24. The method of claim 16, wherein step (c) comprises administering one or more selected from the group consisting of an immunomodulatory agent, physical therapy, occupational therapy, speech therapy, septin-5 specific tolerance induction strategy, and an immunotherapy targeting septin-5-specific T cells and/or B cells.
 25. A kit, comprising: a septin-5 polypeptide, and an anti-IgG antibody.
 26. The kit of claim 25, wherein said anti-IgG antibody is an anti-human IgG antibody.
 27. The kit of claim 26, wherein said anti-human IgG antibody comprises a covalently attached label.
 28. The kit of claim 25, wherein said kit comprises an anti-septin-5 antibody.
 29. The kit of claim 28, wherein said septin-5 antibody is an anti-human septin-5 antibody.
 30. A method of treating a mammal having an autoimmune ataxia associated with septin-5-specific autoantibodies, wherein said method comprises: (a) withdrawing a biological fluid from the mammal, wherein the biological fluid. contains septin-5-specific autoantibodies; (b) contacting said biological fluid with a septin-5 polypeptide to remove a substantial portion of said septin-5-specific autoantibodies from said biological fluid; and (c) returning the biological fluid to the mammal.
 31. The method of claim 30, wherein said mammal is a human.
 32. The method of claim 30, wherein said biological fluid comprises blood.
 33. The method of claim 30, wherein said autoimmune ataxia is an autoimmune cerebellar ataxia.
 34. The method of claim 24, wherein the immunosuppressant is selected from the group consisting of corticosteroids, mycophenolate mofetil, azathioprine, tacrolimus, cyclophosphamide, rituximab, mTOR inhibitors, methotrexate, anti-CD19 monoclonal antibodies, and anti-I1-6 monoclonal antibodies. 